This invention is directed to a power transmission device which includes trunnion and bearing sets for interconnecting the driving shaft of a power generating unit to a driven shaft of an operating unit in order to perform a mechanical function.
The mechanical transmission of power normally requires a transfer device which couples the power generating unit (source) to the operating unit in order to perform a mechanical function. The transfer device simultaneously couples the two units and transfers power between them. Most often, shafts are used in power transmission and are joined by the transfer device for rotational and/or reciprocating energy transfer. This arrangement is often referred to as a "drive shaft" and the transfer device is commonly called a "universal joint" where four (4) trunnions are utilized or a "tripot" where three (3) trunnions are used. The name "universal joint" is most commonly used when referring to any power transfer device regardless of the number of trunnions.
A drive shaft will normally utilize two universal joints whereas a "drive line" may use in excess of two universal joints and shafts.
The universal joint functions to (a) transmit a high starting or high stopping torque including a reversal of direction of rotation, (b) maintain a continuous transfer of power at either constant or varying drive shaft revolutions per minute, and (c) maintain a maximum power transfer between the power source and the operating unit or units during all relative drive line angle and length variations and vibrations.
A common universal joint in use today is that which is sometimes referred to as the Hooke universal joint. In the Hooke joint, the driving and driven shafts are each provided with a yoke, the respective yokes being interconnected by a cross comprised of trunnion-bearing sets. A plurality of transfer surfaces, essentially cylindrical in shape, are ground at the respective trunnions of the cross. Each trunnion transfer surface is adapted to receive a bearing cup which is provided internally with a plurality of needles. Crosses with four (4) transfer surfaces (trunnions) are in widespread use in rear wheel drive vehicles and industrial drive shafts. Similarly, tripots with three (3) transfer surfaces (or trunnions) are in widespread use in front wheel drive vehicles.
The needles used in bearing cups of prior art universal joints serve the function of reducing friction between the trunnion and the bearing cup by rolling, thereby accommodating the relatively slight movement between these members. The needles further serve the function of transferring and maintaining the transmission of torque forces between the bearing cup and the trunnion.
The use of needles in bearing cups is satisfactory insofar as the transmission of torque thru the universal joint. Needles, however, have two (2) principal drawbacks.
First, needles add a cost factor in the manufacture of universal joints both in the cost of the needles themselves and in the cost of assembly of a trunnion and bearing set due to the necessity of handling the needles in assembly. A second drawback, insofar as needles, is the fact that unless sufficiently lubricated, they will eventually wear and deteriorate to the point that the trunnion and bearing set of the universal joint must be replaced.
Somewhat similar problems are encountered in roller tappets for internal combustion engines. In particular, roller tappets are used in engine valve trains to eliminate the sliding action between the tappet and the camshaft. The rollers currently used employ needle bearings with the cost and assembly disadvantages discussed above.
The primary object of this invention is to eliminate the necessity for needles, balls or other rolling members between a trunnion and a bearing cup in a universal joint or between the shaft and roller in a roller tappet assembly.
It is a further object of this invention to eliminate the necessity for introducing lubricants such as greases and oils in a universal joint, which lubricants are normally required to insure low friction in the joint.